The present invention relates to (Cell Delay Variation) CDV-reducing algorithm circuit self-monitoring systems in shaping function systems.
It is well known in the art that an ATM network should have a commonly termed shaping function to alleviate a burst character causing reduction of its utility. The shaping function has resort to a CDV-reducing algorithm. CDV-reducing algorithms are realized by hardware logic circuits. Hereinunder, such a hardware logic circuit is referred to as CDV-reducing algorithm circuit.
In a CDV-reducing algorithm circuit, the transmission time, i.e., instant of transmission, of an input cell is determined from minimum inter-cell interval T.sub.s, permissible residual CDV .tau..sub.s, cell arrival time ta, theoretical next cell transmission time TET under shaping function, ideal cell transmission time t.sub.o derived from shaping and arrival time of a cell immediately proceeding the VP of the input cell, and written in a shaping buffer at a position thereof corresponding theretoto.
FIG. 4 is a flow chart illustrating a process in a CDV-reducing algorithm circuit. In a step 11, initial parameter data (T.sub.s, .tau..sub.s, TET=t.sub.a and t.sub.o =t.sub.a) are set. When the arrival of a cell at time t.sub.s is detected in a step 12, parameter data corresponding to VPI (VCI) is read out in a step 13, and then a step 14 is executed.
In the step 14, a check is made as to whether the detected arrival cell is a user's cell or a non-user's cell. In the case of a user's cell, a step 15 is executed, in which a check is made as to whether theoretical cell transmission time TET is greater than the sum of cell arrival time t.sub.s and permissible residual CDV .tau..sub.s. In the case when the arrival cell is a non-user's cell, an operation which will be described late is brought about.
When the theoretical cell transmission time TET is not greater than the sum of the cell arrival time t.sub.a and the permissible residual CDV time .tau..sub.s, a step 16 is executed, in which the theoretical cell transmission time TET is set to a predetermined time, i.e., max (t.sub.a, TET). Then, in a step 17 an ideal cell transmission time t.sub.o is set to the cell arrival time t.sub.a, and then a step 18 is executed.
When the theoretical cell transmission time TET is greater than the sum of the cell arrival time t.sub.s and the permissible residual CDV .tau..sub.s, the routine goes to a step 19, in which the ideal cell transmission time to is set to the sum of the theoretical cell transmission time TET and the permissible residual CDV .tau..sub.s, and then the step 18 is executed. In the step 18, the theoretical cell transmission time TET is updated by minimum cell time Ts.
When it is found in the step 14 that the arrival cell is a non-user's cell, the routine goes to a step 110, in which the time relation between the ideal cell transmission time T.sub.a and the cell arrival time t.sub.a is checked. When the cell arrival time t.sub.a is found to be later than the ideal cell transmission time t.sub.o, a step 111 is executed, in which the ideal cell transmission time t.sub.o is set to the cell arrival time t.sub.a, and then a step 112 is executed. When the cell arrival time t.sub.a is found to be earlier than the ideal cell transmission time t.sub.o, a step 112 is executed. In the step 112, the ideal cell transmission time is set t.sub.o, and the routine goes back to the step 12.
The CDV-reducing algorithm circuit as described above with reference to the flow chart of FIG. 4, has five different operation patterns #1 to #5 as shown in FIG. 5. These operation patterns #1 to #5 are labeled as #1 to #5 in the flow chart of FIG. 4.
The above CDV-reducing algorithm circuit can guarantee an ideal cell transmission interval to a certain extent.
However, when an abnormal operation result is produced, which is attributable to hardware of the CDV-reducing algorithm circuit, accurate shaping becomes impossible. Accordingly, it is necessary to provide a mechanism, which can detect an abnormality as soon as the occurrence thereof, and producing an alarm for early removal of the abnormality and restoration of the circuit. In addition, it is necessary to detect an abnormality without interrupting the shaping operation but in an in-service state of the circuit.